odysseus42
New member
- Joined
- Oct 25, 2020
- Messages
- 6
- Points
- 3
I'm new to this forum and recently gained interest in laser shows, and I'm currently in the middle of experimenting with modulation circuitry with an arduino. A while back I got one of those 20kpps galvo scanner sets from ebay and an RGB laser module capable of analog modulation.
Since the arduino is not capable of a 0-5V true analog output, I was thinking about using PWM for intensity modulation. I was planning to use an RC low pass filter on the PWM pin, with a transistor used to control the blanking signal connected to another digital pin, since the settling time for the filter would be way too slow in comparison with the blanking times.
But I thought, what if its possible to control both blanking and intensity on the same pin? I know that the PWM frequency would need to be much higher than the scanning speeds, so that the lines drawn in the image won't appear dotted, but I'm not sure by how much. After having read many informative posts (threads listed below), I have an idea that it must be in the MHz range.
I'm almost certain that this is not practical, as there are plenty of ways to generate an analog voltage signal (such as a DAC), but I was trying to be conservative about how many pins on the arduino I was using, since a lot of them are already being used for the DAC circuit for the galvo signals. And I'm also curious if its possible to get more than 7 colors with PWM intensity control if I had a TTL modulated laser. Since DPSS lasers usually can't modulate with MHz frequencies, I would probably have to use an AOM, as per LSRFAQ's posts.
But assuming I have all the necessary equipment for MHz modulation (and a microcontroller that's capable of generating PWM frequencies that high, so not an arduino), what's the relationship between the galvo scanning speeds and modulation frequency for intensity control so that the lines drawn in an image don't appeared dotted, if there is any such relationship?
I did a rough order of magnitude estimation, assuming 30kpps so the time from one point to the next is 1/30000s (I'm still a bit uncertain about this), and assuming that the PWM frequency would need to occur 90Hz within that amount of time so the line appears smooth, which comes out to be (1/30000)/90 = 2.7 MHz. But this would obviously depend on the throw distance and the distance between the points to be drawn. Any advice is appreciated, as I probably have many misconceptions about this topic.
Referenced threads:
laserpointerforums.com/threads/question-about-galvo-speed.71998/
laserpointerforums.com/threads/maximum-modulation-frequency.73401/
laserpointerforums.com/threads/modulation-frequency-for-green.53107/
Since the arduino is not capable of a 0-5V true analog output, I was thinking about using PWM for intensity modulation. I was planning to use an RC low pass filter on the PWM pin, with a transistor used to control the blanking signal connected to another digital pin, since the settling time for the filter would be way too slow in comparison with the blanking times.
But I thought, what if its possible to control both blanking and intensity on the same pin? I know that the PWM frequency would need to be much higher than the scanning speeds, so that the lines drawn in the image won't appear dotted, but I'm not sure by how much. After having read many informative posts (threads listed below), I have an idea that it must be in the MHz range.
I'm almost certain that this is not practical, as there are plenty of ways to generate an analog voltage signal (such as a DAC), but I was trying to be conservative about how many pins on the arduino I was using, since a lot of them are already being used for the DAC circuit for the galvo signals. And I'm also curious if its possible to get more than 7 colors with PWM intensity control if I had a TTL modulated laser. Since DPSS lasers usually can't modulate with MHz frequencies, I would probably have to use an AOM, as per LSRFAQ's posts.
But assuming I have all the necessary equipment for MHz modulation (and a microcontroller that's capable of generating PWM frequencies that high, so not an arduino), what's the relationship between the galvo scanning speeds and modulation frequency for intensity control so that the lines drawn in an image don't appeared dotted, if there is any such relationship?
I did a rough order of magnitude estimation, assuming 30kpps so the time from one point to the next is 1/30000s (I'm still a bit uncertain about this), and assuming that the PWM frequency would need to occur 90Hz within that amount of time so the line appears smooth, which comes out to be (1/30000)/90 = 2.7 MHz. But this would obviously depend on the throw distance and the distance between the points to be drawn. Any advice is appreciated, as I probably have many misconceptions about this topic.
Referenced threads:
laserpointerforums.com/threads/question-about-galvo-speed.71998/
laserpointerforums.com/threads/maximum-modulation-frequency.73401/
laserpointerforums.com/threads/modulation-frequency-for-green.53107/